Coupling device



July 5, 1932. c. FICHANDLER COUPLINGQDEVICE Filed April 21, 1930 Patented July 5, 1932 UNITE STATES CARL FICHANDLER, Oil? NEW YORK, N. Y..

COUPLING DEVICE Application 'filed .April 21,

r In radio frequency amplifiers and similar apparatus it is necessary to regulate the "amount of energy transfer from one part of the electrical system to another. .This regun lation may be accomplished in steps or by a continuously variable means;v the latter being c'onsideredthe most desirable for use in broadcast radio receivers. It is with this latter type of continuous volume control that this invention deals primarily, although'its principle applies to step by step regulators .as well. The features and advantages-of a volume control system embodying all the principles of the present invention will be 7:: made clear by an analysis of the methods now commonly'used for volume control in broadcast receivers. r

In the great majority of radio sets volume -=control is-ac'complished by means of a va- 2H riable resistor of the sliding contact type;

generally a slide-wire rheostat or potentiom- 'eter. Now, strictly sjfieaking every slide-wire instrument is a non-continuous 1 (step by step) instrument, the size of the step being the resistance of a single full turn of wire from contact point to contact point. While themagnitude of the resistance of one of such single turns of wire between the contact points is insignificant at regions of high total resistance, this dis-continuity becomes very disturbing at the zero end'of rheostats. 'It is a well known fact that most of the 'powerful'radio sets now on the market are unable to reduce to a sufficiently low value 7 the signals from high powered local transmitters, the volume jumping from zero to an undesirably high amount with the most minute adjustment that can be made,

This dis-continuity is'theo'retically avoided in certain carbon composition rheostats which vary the contact point either directly by a sliding metal spring, or in an alternative form indirectlyrby acurved disc rolling over the carbon disc under the pressure of a sliding spring. All rh'eostats, however, share the 1930; Serial 110,446,128. o big drawback of relying upon the electrical contact maintained bya mechanical spring pressure. It has been found in practice that all such contacts deteriorate, through corrosion of the metal surfaces, wearing of bearat) ings, aging of carbon, loosening of springs, and other, effects. The results of this deterioration of rheostats results in the characteristics highly objectionable crackling noises heard'in all radios sets after .a few months of use. In addition, it will be shown below that rheostat control shares with other known controlling means, the disadvantage of. changing the resonant frequency of tuned circuits. As an alternative to Volume-control :by re- 131) I sistance variation, there remains the reactance control, which involves the variation of inductance of capacity, While 1t is true that the variation of reactance can be accomplished without discontinuity and ith tew sliding pressure contactsfby virtue of'the use of the well known variometers, variocouplers, and variable condensers; yet, this scheme has the disadvantage of changing the tuning of the circuits as the reactances 74) are varied. v

Thus, 1f a valuation in reactance is used to detune a'loosely coupled resonant circuit,

an eitectivevolume control will be had, but onlyat the cost of selectivity and ualit-y. The slight detuning necessary'for the esired change of energy transfer issufiicient to cause objectionable side-band-cutting in a receiver of; audio "frequency modulated radio frequency-signals, 1 1

Moreover, in receivers of, averagesharpness of resonance this slight detuning toaef- -fect volume control will also shift the resonance point of the detuned circuit-beyond'the 10' kilocycle tuning channel "assignedito lthe broadcasting stations, thereby tending to bring in disturbing signals from adjacent signal channels. V 1

.Again, if the'variable reactanceis used' i-as a coupling reactance, for instance between "sistance variation as described above.

the antenna circuit and the first tuned radio frequency stage, or between a plate circuit of one amplifier tube and a tuned grid circuit of a succeeding amplifier tube, it might appear offhand that the variation of coupling will cause variation in volume without detuning. As a practical matter, this is not so for the following reasons: The primary (or driving) circuit, containing the antenna or the plate impedance of a tube, has a definite reactance of its own; and the same coupling. reactance which transfers varying amounts. of. energy from the primaryrcircuit into the secondary, also transfers into the secondary varying fractions of the primary impedance. If Z is the primary impedance, M the common coupling impedance which may be inductive, capacitive or even resistive, then the impedance (Z transferred into the secondary circuit from the primary is: 1 I f ,Eguation (1) s ZFTZT 1' Consequently, cannot vary either Mor Z without simultaneously varying Z thus detuning the secondary circuit. To a lesser degree, this is also true for most of the above mentioned volume controls based upon rethe circuit, the resistance of which is changed,

is in any waycoupled to a tuned circuit, it changes the resistance of that tuned circuit; and since the resonance frequency F of a circuit containing a resistance R, an inductance L, and a capacitance C is expressed by Equation (2) Zr rein ing is affected by a change in'R.

. It is therefore an object of this invention to provide a volume control, utilizing a con -tinuously variable reactance designed to effect theenergy transfer from a primary driving circuit into a secondary driven circuit, oneor both of which are tuned to the fre- 'quency of the desired signal, without such variations in .reactance changing the tuning ,ofthe coupled circuits. It is afurther object of this invention to provide a volume control utilizing a variable reactance in combination with a compensating reactance, both of which are constructed and arranged to give volume control without changing the tuning.

1 f It is also'now well known and understood .in this art that the tendency of a radio frequencyamplifier to go into self oscillation depends, among other things, upon the value of the plate inductance of each amplifier 7 stage. r

It has been found that a radio receiving set constructed in accordance with the principles of this invention has the further advantage that the tendency toward self oscillation of the amplifier stage is greatly reduced by virtue of the fact that variations in coupling and tuning which ordinarily alter the value of the plate inductance of the amplifier tube do not effectively alter the value of the plate inductance of the amplifier tube of a system constructed in accordance with this invention.

It is therefore a further object of this invention to provide, in a radio receiver utiizing radio frequency amplifiers, a means for varying the tuning of the amplifier stages and also for varying the amount of energy transfer between stages, without producing attendant undesirable variations in the plate impedance of the amplifier tubes.

Further, it is an object of this invention to provide radio receiving set employing radio frequency amplifiers, in which volume control is effected by variation of certain reactances, while at the same time compensating the tuned circuits for such variations, in such a way as to avoid detuning and to avoid also the tendency toward self oscillationof the amplifiers.

These and other objects of the invention will be readily apparent to those skilled in the art from the following description taken in connection with the accompanying drawing in which:

Fig. 1 is a diagrammatic representation of a system embodying the principles of this invention; and

Fig. 2 is a modification.

Briefly, the objects of this invention are realized by virtue of a compensating reactance which is coupled to the variable reactance which efiects the volume control in such a way that the detuning action of the volume control per se is compensated for by the auxiliary reactance.

Let us assume, for example, that the vol ume control consists of a variable mutual inductance M coupling a driving circuit having an impedance Z and a tuned secondary circuit. Let us assume further that the compensating circuit has an im 3Clt210 Z and is coupled to the tuned circuit by a variable mutual inductance N. I have found that compensation is achieved if the following relationship exists:

Equation 2 2 g =constant Equation (4) Referring in detail to- Fig: '1. of the draw-' ingthere is shown an arrangement-'embody ing'tli'eprinciples .otth is inventionp The primary circuit in this -caseillustratedconsists ot theplate impedance of an amplifier tubeP in series with the self inductance ofa coupling coil m. The "battery B for supplying -the high potential to the tube]? is ,shunted'by a condenser is," thus eli'minating the resistance-ofthe-battery B- to the-fiow ot radio frequency] currents in the plate circuit. The secondarycircuit comprises the input circuit of a second amplifier tube Q.

This input circuit includes-the inductance Ii whichis variablycoupled to the coil m. A

compensating coil n -is coupled to the coil-L. Since in the primarycircuit the plate impedance is' equivalent to a'resistance r shunted-bytheplate capacity o the compensating circuit also includes ares'istor m and parallel with-acondens'e'r o The-coils meand a are mounted upon a common shaft" so thatthe couplingbetween the coils m and L and n andxL may be simultaneously varied. 'That is; as the-coupling between m and L is reduced the---coupling between a and L is increased; To obtain the desired variations in coupling between the coils any suitably shaped variometers maybe used; or alternatively, any

" suitably shaped camstructures-may be used to provide-for variations of coupling in accordance with any desired predetermined law; The. amplifiertube Q, is tuned by means of the variable condenser S. The condenser S ma-y be one of a gang otcondensers used to vary the tuning of a cascaded radio frequency -amplifier. T r In this event all of the condensers are usually operated from a common shaft by the well known uni-"control means; 'It is also contemplated byth-is invention that the unicontrol ior the variable tuning condensers be-coupled to the variable coupling means,

so that variablecoupling maybe had with variable tuning, the compensating impedance servin'goto permit simultaneous variations in coupling-and tuning by single means. It will be'understood that provision should be madewhereby thetuningvariations and con pling variations-including the compensating means-may be'made either together or separately, and that when they are made together the coupling isvaried'with the tuning to givethe most efic'ient transfer of energy, Whereas when it is desired to Vary the coupling as: a volume control means alone the tuning adjustmentshould'not be-altered; It will be understood, of course, that in the case where I vary the coupling and tuning-to wi h gether by a single means, my compensating device functions to counteract changes in impedance caused solely by changes in coupling and therefore the changes in coupling do: not affect the operation otthe uni-con trol tuning adjustmentsv I' h'ave shown diagrammaticallyin Fig. thevariable elements of the coupling coils, tuning condensers, and

compensating device as being coupled to-- gether for concomitantoperation.. In'pra'c-' tice anyof the well known mechanical arrangements may be used. To permit independent adjustment of the variable coupling; means and the variable tuning means, any

suitable mechanical arrangement may be used.- v

The constants of the compensating circuit.

of Fig. 1 are adjusted to maintain the following relation:

Equation. (5) v -N:1*,-.: 0,.=M :r 0

Furthermore, the relative positions on the control shaft of the coils 'm and 7b are sochosen that their mutual inductances to L re main in accordance with Equation Referring to Fig. 2,anotherembodiment of the same invention is shown; circuit in thiscase is the antenna A. The

coupling impedance is the small variable The driving circuit counteract those of the antenna cir-' cuit.. This is most easily achieved by mak- Equation (5a) 651:0! I Where C capacity of antenna or primary circuit j H Equation (5b) I n a where R =resistance of antenna orprimary circuit.

Equation. (50) where L the inductance of the antenna or primary I circuit Equation (3a) 0 constant 0 It is evident that there are many possible variations of the circuit "described above which can be designed by any one 'skilled'in the art. For instance, therimpedance ofithe primary: of .two :couple'd circuits is afiected 5 circuit variably coupled to said first circuit,

, is produced in said first circuit a change in for coupling variations by the secondary impedance in the same way as the secondary is affected by thep'rimaryg In this event, it. is'merely necessary to apply the compensat-- ing circuit toithe primary circuit, applying the principles outlined above, in stead of applying the compensating circuit to the secondary. It is also Wltlllll, the scope of this invention to apply the compensating circuit both to the primary and the secondary cir cuits following the principles already mentioned.

Having thus described my invention, what I claim is:

1. A variable coupling device comprising in combination, a first tuned circuit, a second circuit coupled thereto, a variable reactance connected to said first circuit for varying the coupling of said circuits, said variation in coupling producing in said tuned circuit a change in the'tuning thereof, a third circuit variably coupled to said first circuit. and means for simultaneously varying the coupling between said first and second circuits and said second and third circuits, in such a manneras to maintain substantially constant the tuning of said first circuit.

2. A variable coupling device comprising in combination, a first tuned circuit, a sec- 7 0nd circuit coupled thereto, a variable react ance connected to said first circuit for varying the coupling of said circuits, said variation in coupling producing in said tuned circuita change in the tuning thereof, a third said third circuit containing reactance elements simulating said second circuit, and means for simultaneously varying the coupling between said first and second circuits and said second and third circuits, in such a manner as to maintain substantially constant the tuning of said first circuit.

3. A variable coupling device comprising a first tuned circuit having an inductance and capacitancetherein, a second circuit vari'ably coupled to said first circuit and having an inductance, a capacitance, and a resistance contained therein, means to vary the coupling of said two circuits, whereby there the value of the inductance contained therein, and means to compensate for the said change in inductance.

4. A'variable coupling device comprising a first tunedcircuit having. an inductance and" capacitance therein, a second circuit variably coupled to said first circuit and having an inductance, acapacitance, and a re sistance contained therein, means to vary the coupling of said two circuits, whereby there is pro-ducedin said first circuit a change in the value of the inductance contained therein, and means to compensate for the said change in inductance, said first mentioned 'means' and said last-mentioned means being mechanically coupled together forconcomitant operation. I

5, A variable coupling device comprising a first tuned circuit having an inductance and capacitance therein, a second circuit variably coupled to said first circuit and having an incuit variably coupled to said first circuit, and means for simultaneously varying the conpling betweensaid first and second circuits andsaid second and third circuits, in such a manner as to maintain substantially constant the'tuning of said first circuit.

6. A variable coupling device comprising a first tuned circuit having an inductance and capacitance therein, a second circuit variably coupled to said first circuit and having an inductance, a capacitance, and a resistance contained therein, means to vary the coupling of said two circuits, whereby there is produced in said first circuit a change in the value of the inductance contained therein, a third circuit variable coupled to said first circuit, said third circuit containing reactance elements simulating said second circuit, and means for simultaneously varying the coupling between said first and second circuits and said second and third circuits, insuch a manner as to maintain substantially constant the tuning of said first circuit.

7. In a radio receiver having a first radio frequency circuit, and a second radio frequency circuit coupled thereto, the combination with a volume control device for regulating the volume of sound reproduced by said receiver, said device including a variable coupling means which introduces variations in tuning in one of said-circuits as the coupling is varied to effect volume control, and means to compensate for such variations in tuning in such a way as to maintain the said tuning independent of said variations in coupling.

7 8. In a radio receiver having a first radio frequency circuit, and a second radio frequency circuitcoupled thereto, the comb-ination with a volume control device for regulating the volume of. soundreproduced by said receiver, said variable coupling device including a condenser having two separated fixed plates and a single rotary plate cooperating therewith, the plates being so arranged that an increase in capacity between two of-such platesis accompanied by a decrease in capacity between one of said two plates and the third plate, and means for moving said rotary plate to control the volume of sound reproduced by said receiver by varying the cow pling between said two circuits, said variations in coupling tending to introduce incidentally variations in tuning of one of said circuits, and said variations in tuning being compensated for by two ofthe plates of said coupling device, in such a way as to maintain substantially constant the tuning of sald circuits as the coupling therehetween is varied;

9. In a radio receiving system including an antenna circuit, a three-plate condenser having two of its plates connected in said antenna circuit, a radio frequency amplifying circuit, a third plate of said condenser being connected to said last mentioned circuit, means to vary the position of said third plate with respect to said other two plates, whereby simultaneously to Vary the coupling between said antenna circuit and said radio frequency amplifier and to maintain substantially constant the tuning of said antenna circuit.

In witness whereof I hereunto aflix my signature.

CARL FICHANDLER. 

